1. Field of the Invention
The present invention relates to a liquid form addition curable silicone rubber composition for a fluororesin covered fixing roller (in other words, fuser roller) used in devices such as copiers, laser printers and facsimiles, and to a fluororesin covered fixing roller with a silicone rubber layer formed from a cured product of such a composition.
2. Description of the Prior Art
Silicone rubber is widely used for the fixing rollers used in devices such as copiers, laser printers and facsimiles. The reason for this prevalence is that in comparison with other rubber materials, silicone rubber displays superior properties of releasability relative to toner, heat resistance and compression set. However, with the recent increases in speed of the above types of devices, a process called oil fusing, in which silicone oil (so-called fuser oil) is supplied to the roller surface, is now used in order to further improve the toner releasability. In addition, in order to increase the time required for fusing at such high speeds, reductions in the hardness of the rubber material are being used as a way of maintaining the fusing width (nip width).
However, because silicone rubber is formed from the same materials as silicone oil, reducing the hardness of the rubber can result in swelling caused by the fused silicone oil. One method for resolving this problem involves preparing a roller from a low hardness silicone rubber or a silicone rubber foam, and then covering the surface of this roller with a flexible coating formed from a fluororubber latex or a fluororesin tube. This type of coating extends the life of the fixing roller markedly, but the problem remains that with the increases in speed of the aforementioned devices, the adhesion interface between the silicone rubber and the fluororesin tube or fluororubber latex, as well as the adhesion interface between the silicone rubber and the cylindrical metal core, are unable to withstand for extended periods the stress generated by high temperatures and deformation.
The present invention is the result of intensive research in view of the issues described above, and has an object of providing a liquid form addition curable silicone rubber composition for a fluororesin covered fixing roller, in which a fluororesin covering layer (a surface mold releasing layer) formed from a fluorine based coating material such as fluororubber latex or a fluororesin tube of PFA, PTFE or FEP or the like, is bonded to a silicone rubber layer, and this silicone rubber is also bonded to a metal core, wherein even if the thus formed roller is used for extended periods, separation of the layers is unlikely to occur. Another object of the present invention is to provide a fixing roller with a silicone rubber layer formed from a cured product of the above type of composition.
In other words, in order to resolve the aforementioned issues, the present invention provides a liquid form addition curable silicone rubber composition for forming a fluororesin covered fixing roller comprising:
(a) 100 parts by weight of an organopolysiloxane with at least two alkenyl groups bonded to non-terminal silicon atoms within the molecular chain of a molecule,
(b) an organohydrogenpolysiloxane with at least two hydrogen atoms bonded to silicon atoms within a single molecule, in a sufficient quantity to produce a molar ratio of silicon atom-bonded hydrogen atoms within the constituent (b) relative to the alkenyl groups bonded to silicon atoms within the constituent (a) of 0.4 to 5.0,
(c) an effective quantity of a platinum based catalyst,
(d) 0.1 to 10 parts by weight of dry process silica, and
(e) 0.05 to 5 parts by weight of a cyclic diorganopolysiloxane with at least three alkenyl groups bonded to silicon atoms within a single molecule.
Furthermore, the present invention also provides a fluororesin covered fixing roller comprising a metal core, a silicone rubber layer formed either directly or indirectly around the outer periphery of the core, and a fluororesin layer (surface mold releasing layer) formed on the outer periphery of the silicone rubber layer, wherein the silicone rubber layer is a cured product of a liquid form addition curable silicone rubber composition as described above.